def show_max_factor(num):
    count = num // 2
    while count > 1:
        if num % count == 0:
            print("%d最大的约数是%d" % (num, count))
            break
        count -= 1
    else:
        print("%d是素数！" % num)


if __name__ == "__main__":
    num = int(input("请输入一个素数："))
    show_max_factor(num)
